Synthesis and characterisation of metal–organic frameworks containing bis(β-diketonate) linkers

Abstract

Four metal–organic frameworks have been isolated and structurally characterised from the reaction between Zn(NO₃)₂·6H₂O and the bis(β-diketone) 3,4-diacetyl-2,5-dioxohexane in the presence of triethylamine. When the reaction was carried out in DMF/chloroform or DMSO/methanol the one-dimensional coordination polymers {[Zn(L)(DMF)]·0.65CHCl₃·0.35DMF}_∞1 and {[Zn₃(L)₃(MeOH)(DMSO)_4.2]·0.8DMSO}_∞2, respectively, were isolated in low yield. When the reaction was carried out in methanol, three products were isolated – {[Zn₂(L)₂(MeOH)₂]·2MeOH}_∞3, {[Zn₂(L)₂(MeOH)]·2H₂O}_∞4 and {[Zn₂(L)₂(OH₂)₂]}_∞5. Compounds 3 and 4 have structures in which Zn₂(μ-β-diketonate)₂(β-diketonate)₂ dimers are interlinked into similar two-dimensional networks. Analyses suggest 5 has a similar structure, though with terminal aqua ligands instead of methanol ligands. The reaction between Cd(NO₃)₂·4H₂O, 3,4-diacetyl-2,5-dioxohexane and triethylamine in methanol gave {[Cd₂(L)₂(H₂O)₂]·2.5H₂O}_∞6, which has a similar network structure to 3 and 4. These compounds are the first structurally characterised network structures based on bis(β-diketonate) ligands, and they demonstrate that these ligands can behave in an analogous manner to dicarboxylates.